Re: [PATCH 3/4] mdadm: Avoid array bounds check of gcc

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Wed, 27 Sep 2023 10:52:18 +0800
Xiao Ni <xni@redhat.com> wrote:

> With gcc version 13.2.1 20230918 (Red Hat 13.2.1-3) (GCC), it reports error:
> super-ddf.c:1988:58: error: array subscript -1 is below array bounds of
> ‘struct phys_disk_entry[0]’ [-Werror=array-bounds=]
> The subscrit is defined as int type. And it can be smaller than 0.

If it can be smaller that 0 then it is something we need to fix.
I think that it comes from here:
		info->disk.raid_disk = find_phys(ddf, ddf->dlist->disk.refnum);
		info->data_offset = be64_to_cpu(ddf->phys->
						  entries[info->disk.raid_disk].
						  config_size);

find_phys can return -1.
It is handled few lines bellow. I don't see reason why we cannot handle it here
too.

		if (info->disk.raid_disk >= 0)
			pde = ddf->phys->entries + info->disk.raid_disk;

I think that it will be fair to abort because metadata seems to be corrupted.
We are referring to info->disk.raid_disk from many places. We cannot return
error because it is void, we can just return.

> To avoid this error, add -Wno-array-bounds flag in Makefile.

If you want do it this way please provide strong justification. We are
disabling check in all code to hide particular case. It will not prevent us
from similar mistakes during development in the future.

Thanks,
Mariusz